Forget Chicago lost to the Lions 21-19 or that it failed to seize first place in the NFC North, Sunday should stand as the signature game of Cutler's career: a symbol of the day when no one here will wonder about his toughness again.

Jay Cutler with a partially torn groin and twisted ankle in the Bears' loss to the Lions. (AP)

No matter how well McCown played against the Packers last Monday night, Cutler is the Bears' best hope for a deep postseason run. He is the Bears quarterback who can fling the ball 50 yards with precision while standing perfectly still. He is the one who will fire passes between defenders and wait for a receiver to come open as the pass rush rumbles in.

When Marshall was asked after Sunday's game what advantage a limping Cutler brought to the Bears he glared at his questioner.

"Let me say it like this: There are not a lot of Jay Cutlers walking the streets," Marshall said. "I'm talking everybody. I don't care how great Josh McCown does. He's awesome. I'm glad we have him as our No. 2, but Jay Cutler is our quarterback. No one can lead our team better than he can, 80 percent of Jay Cutler is better than a lot of guys at 100 percent in the NFL."

For much of his time with the Bears, Cutler has been an awkward presence for the public. He struggled playing for a defensive-minded head coach and a rotation of offensive coordinators who all proclaimed to be his savior but instead disrupted his progress with new offenses that took time to master. The NFC title game scarred his image even as many of the Chicago players understood.

It has taken Trestman – who has nurtured quarterbacks from Bernie Kosar to Steve Young to Jake Plummer – to steady Cutler, to turn him from a sports radio punch line to the most essential piece of a playoff push. And after Sunday no one should doubt his value to the Bears.

Chicago should have won this game. It should have won because of a third-quarter throw Cutler made near the goal line that bounced off the hands of receiver Alshon Jeffery. It should have won because of a fourth-quarter toss Cutler made to the back of the end zone that Jeffery momentarily caught jumping over two defenders before juggling as he fell to the ground. It should have won on a long pass Cutler made to Marshall that was just a few inches too far from Marshall's outstretched hands.

Cutler was 21 of 40 for 250 yards with one touchdown and an interception. (USA Today)

And he did all this while being knocked to the ground, hit in the helmet and bumped in the groin by the charging Lions pass rushers. At some point in the second quarter he turned his ankle. Trainers frantically wrapped it and taped it at halftime. When Trestman asked Cutler if he could play the second half, the quarterback said yes. But as the blows from the Lions came – all of which he called "normal football" – he wobbled. He limped. His throws lost zing. Still he fought.

"He led us," Marshall said.

Some will want to make Sunday about a quarterback who shouldn't have been playing. Some will look to Trestman and see a coach whose zeal to seize first place in the NFC North forced him to play a quarterback who wasn't healthy. But this is not a Mike Shanahan-Robert Griffin III moment. Trestman is too careful of quarterbacks to push Cutler into a game in which he did not belong. The biggest thing his quarterbacks always say about him is that they trust him.

At one point on Sunday Cutler, feeling restricted in his movements, turned to his coach and asked: "Do I look OK? Am I still getting it done?"

Trestman left him in. The trainers told him Cutler couldn't hurt the groin or the ankle any more and he had made too many good throws that hadn't been caught.

"I'll look at the tape and see what the tape shows," Trestman said. "I may come back tomorrow and say 'I made a mistake, I should have taken him out earlier.' "

Which is something most NFL coaches wouldn't have the courage to do. And it is why Trestman's quarterbacks believe in him.

When Trestman finally did pull Cutler it was because the Bears were down eight points with 2:22 left, and both coach and player knew a two-minute drill needed a quarterback more mobile than Cutler at that point. By then, nobody was going to question Cutler's willingness to play with pain.